1. Field of the Invention
The present invention relates to an infrared ray sensor driving circuit, and particularly to an improved infrared ray sensor driving circuit capable of advantageously controlling an amplifying level and a cut-off frequency of a filter by separating the functions of an amplifier and a filter, respectively.
2. Description of the Conventional Art
Referring to FIG. 1, there is shown a first conventional infrared ray sensor driving circuit. As shown therein, the conventional circuit includes an impedance matching stage 1 for matching the output impedance of the signals of the infrared ray generated from a human body with an input impedance of the infrared ray sensor driving circuit, a first amplifying stage 2 for filtering the signals outputted from the impedance matching stage 1 and for amplifying the filtered signals by a predetermined amount, and a second amplifying stage 3 for filtering the signals outputted from the first amplifying stage 2 and for amplifying the filtered signals by a predetermined amount.
Here, in the impedance matching stage 1, series-connected condensers C1 and C2 are connected in parallel with a resistor R1 between a gate of a field effect transistor FET and ground. The supply voltage VDD is applied to a drain of the field effect transistor FET, and a condenser C3 is connected to the drain of the field effect transistor FET, and a resistor R2 is connected between the source terminal of the field effect transistor FET and ground.
In the first amplifying stage 2, the source of the field effect transistor FET of the impedance matching stage 1 is connected to a non-inverting input terminal (+) of a first amplifier OP1, and a condenser C5 and a resistor R4 in parallel are connected between an output terminal of first amplifier OP1 and an inverting input terminal (-) thereof, and a resistor R3 in series with a condenser C4 are connected between the inverting input terminal (-) of first amplifier OP1 and ground.
In the second amplifying stage 3, the output terminal of the first amplifier OP1 of the first amplifying stage 2 is connected to a non-inverting input terminal (+) of a second amplifier OP2, and a resistor R6 and a condenser C7 are connected in parallel between an output terminal of the second amplifier OP2 and an inverting input terminal (-) thereof, and a resistor R5 in series with a condenser C6 are connected between the inverting input terminal (-) of second amplifier OP2 and ground.
Referring to FIG. 2, shown therein is a second conventional infrared ray sensor driving circuit which includes an impedance matching stage 1' for matching the output impedance of the signals detected from the infrared ray generated from a human body with the input impedance of the infrared ray sensor driving circuit, a first amplifying stage 2' for filtering the signals outputted from the impedance matching stage 1' and for amplifying the filtered signals by a predetermined amount, a second amplifying stage 3' consisting of a second amplifier OP2, diodes D1 and D2, condensers C7 and C9 and resistors R5, R6, R12, and R13, for filtering the signals outputted from the first amplifying stage 2' and for amplifying the filtered signals by a predetermined amount, a comparator stage 4 consisting of first and second comparators CP1 and CP2 and diodes D3 and D4, for comparing the level of the signal outputted from the second amplifying stage 3' and the value of the supply voltage VDD, a pulse generating stage 5 for generating pulses in accordance with the signals outputted from the comparator stage 4, and a relay driving stage 7 consisting of a transistor Q1 and resistors R9 and R10 for driving a relay 6 in accordance with the pulses outputted from the pulse generating stage 5.
Referring to FIG. 2, the detailed operation of the second conventional infrared ray sensor driving circuit will now be explained.
To begin with, the infrared ray sensor 1a, which detects the infrared ray generated from a human body, requires the impedance matching stage 1 in order to convert the impedance of the detection signals through the field effect transistor. Here, since the output impedance of the infrared ray sensor 1a is relatively high and the level of the detected signals is weak, the impedance of the signals outputted from the infrared ray sensor 1a is converted.
Thereafter, the signals converted in impedance from the infrared ray sensor 1a are applied to the non-inverting terminal (+) of a first amplifier OP1 of the first amplifying stage 2' from the source of the field effect transistor.
In addition, the first amplifier OP1 in the first amplifying stage 2' non-invertingly amplifies and filters the signal applied thereto by a predetermined amount of 1+[(.omega.C4.multidot.R4)/(1+.omega.C4.multidot.R3)(1-.omega.C5.multidot. R4)], and then the amplified and filtered signal is applied via condensers C9 and resistor R5 to the inverting input terminal (-) of the second amplifier OP2 in the second amplifying stage 3' from the output terminals of the first amplifier OP1.
The second amplifier OP2 invertingly amplifies and filters the inputted signal by a predetermined amount of 1+[(.omega.C9.multidot.R6)/(1+.omega.C9.multidot.R5)(1-.omega.C7.multidot. R6)] as the signal is applied to the inverting input terminal (-) of the second amplifier OP2, and the amplified and filtered signal is outputted through the output terminal of the second amplifier OP2 and applied to the non-inverting input terminal (+) of the first comparator CP1 and the inverting input terminal (-) of the second comparator CP2, respectively in the comparator stage 4.
Thereafter, the first comparator CP1 in the comparator stage 4 compares the value of the signal received at its non-inverting input terminal (+) with the voltage dropped from supply voltage VDD across the resistor R12 and applied to its inverting input (-) and outputs the compared value to the anode of the diode D3.
Meanwhile, the second comparator CP2 of the comparator stage 4 compares the value of the signal received at its inverting input terminal (-) with the voltage value of supply voltage VDD dropped through the resistor R12, diodes D1 and D2 and dividing the resistor R13 all connected in series to ground.
Here, if the output level of the first comparator CP1 is high, the output level of the second comparator CP2 becomes low, so that the high level output of CP1 is applied to the anode of the diode D3 to bias diode D3 into forward conduction and is conducted thereby to an input port P4 of the mono-stable oscillator 5a of the pulse generating stage 5, while, conversely, if the output of comparator CP2 is high level, it is passed to input port P4 of oscillator 5a through the diode D4.
Thereafter, the mono-stable oscillator 5a of the pulse generating stage 5 generates pulses in accordance with the signals outputted from the first and second comparators CP1 and CP2 of the comparator stage 4 and applies the pulses to the base of the transistor Q1 of the relay driving stage 7 its output terminal P6. Here, the transistor Q1 of the relay driving circuit 7 is turned on or off in accordance with the signals applied to its base.
Here, when the output from the mono-stable oscillator 5a is a high level pulse signal, the transistor Q1 which receives the high level signal at its base is turned on and then the supply voltage VDD is conducted through the relay coil RYC of the relay 6 to ground through the transistor Q1.
Thereafter, the relay switch RYS of the relay 6 is turned on and an instrument(not shown) is activated thereby.
Meanwhile, when the output from the mono-stable oscillator 5a is a low level signal, the transistor Q1 receiving the low level signal at its base is turned off. Thereafter, the supply voltage VDD from the relay coil RYC is applied to the light-emitting diode LED and then the light-emitting diode LED is lighted and the relay switch RYS is turned off.
However, the conventional infrared ray sensor driving circuit concurrently performs the filtering and amplifying, so that the gain of the amplifier and the cut-off frequency of the filter cannot easily be controlled. That is, if a resistance value is changed in order to change the gain of the amplifier, the cut-off frequency is changed thereby, and on the contrary, if the cut-off frequency of the filter is changed, the gain of the amplifier is changed thereby. In addition, since the filter exhibits only one pole, good performance for noise prevention cannot be obtained.